Quad-clutch multi-speed transmission

ABSTRACT

A transmission has a first and a second planetary gear set with four input torque-transmitting mechanisms, such as friction clutches, to achieve torque flow through the planetary gear sets to a countershaft gearing arrangement. The transmission includes an input member, an output member, a pair of planetary gear sets, an input clutch assembly having four input clutches and a countershaft gearing arrangement. The countershaft gearing arrangement is operatively connected with the planetary gear sets and includes: three co-planar intermeshing gear sets, first and second countershafts, a first intermediate shaft, a second intermediate and a third intermediate shaft concentric with the input shaft.

TECHNICAL FIELD

The invention relates to a multi-speed transmission having a quadruple input clutch selectively connectable to a pair of planetary gear sets and a countershaft gearing arrangement.

BACKGROUND

A typical multi-speed, dual clutch transmission uses a combination of two friction clutches and several dog clutch/synchronizers to achieve “power-on” or dynamic shifts by alternating between one friction clutch and the other, with the synchronizers being “pre-selected” for the oncoming ratio prior to actually making the dynamic shift. “Power-on” shifting means that torque flow from the engine need not be interrupted prior to making the shift. This concept typically uses countershaft gears with a different, dedicated gear pair or set to achieve each forward speed ratio (with the exception of being able to achieve a direct drive ratio in a rear wheel drive application). Accordingly, the total number of gears required in this typical design is two times the number of forward speeds, plus three for reverse. This necessitates a large number of required gear pairs, especially in transmissions that have a relatively large number of forward speed ratios. Thus, a need exists for a more compact efficient transmission that utilizes gear pairs.

SUMMARY

A transmission is provided having a pair of planetary gear sets with a quadruple input torque-transmitting mechanism, such as friction clutches, to achieve torque flow through the pair of planetary gear sets to a countershaft gearing arrangement. The transmission includes an input member, an output member, a pair of planetary gear sets, a quadruple input clutch assembly having a first, second, third and fourth torque-transmitting mechanisms and a countershaft gearing arrangement.

The pair of planetary gear sets have a first, second and third members. The first, second, third and fourth torque-transmitting mechanisms of the quadruple input clutch assembly are each selectively engageable to connect the input member with a respective different one of the members of the pair of planetary gear sets.

The countershaft gearing arrangement is operatively connected with the pair of planetary gear sets and includes: three sets of co-planar intermeshing gears, a first intermediate shaft, a second intermediate shaft and a third intermediate shaft, a plurality of synchronizers and first and second countershafts. The first intermediate shaft is connected for common rotation with the sun gear member of the planetary gear set. The second intermediate shaft is connected for common rotation with the carrier member of the planetary gear set. The third intermediate shaft is connected for common rotation with the ring gear of the planetary gear set.

The first and second countershafts are radially offset from and typically parallel to the intermediate shafts. The plurality of synchronizers are selectively engagable to connect selected ones of the gears of the co-planar gear sets with selected ones of said shafts for common rotation to thereby transfer torque from the planetary gear set to the output members along the shafts and the sets of co-planar intermeshing gears.

The first and second countershafts each has a countershaft transfer gear rotationally fixed to the respective countershaft. The countershaft transfer gears each mesh with an output transfer gear that is connected to the output member.

The planetary gear set may be a beveled gear set, a simple pinion or a double pinion (compound) planetary gear set.

In another aspect of the invention, a reverse torque ratio may be achieved by utilizing a brake that selectively connects the carrier member of the planetary gear set to a stationary member to obtain a reverse torque ratio, thus eliminating the need for a dedicated set of intermeshing gears.

Thus, the present invention reduces the number of layshaft gears required for a given number of different gear states by “re-using” some or all of the physical gears in more than one gear state.

The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an embodiment of an nine speed transmission having a quadruple input clutch assembly connected to a pair of planetary gear sets and a countershaft gearing arrangement, in accordance with the present invention;

FIG. 2 is a truth table listing the engaged torque-transmitting mechanisms and synchronizers for selected torque ratios achieved by the nine speed transmission of FIG. 1;

FIG. 3 is a schematic representation of an embodiment of a nine speed transmission having a quadruple input clutch assembly connected to a pair of planetary gear sets and a countershaft gearing arrangement in accordance with the present invention; and

FIG. 4 is a truth table listing the state of engagement of the torque-transmitting mechanisms and synchronizers for selected torque ratios achieved by the nine speed transmission of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components, in FIG. 1 a multi-speed transmission 10 is depicted. The transmission 10 includes an input member 12 and output member 14. In the present embodiment, input member 12 and output member 14 are shafts, and will be referred to as such. Those skilled in the art will appreciate that the input and output members 12, 14 may be components other than shafts. The input shaft 12 is continuously connected to an engine (not shown) or to a turbine of a torque converter (not shown). The output shaft 14 is continuously connected with the final drive unit (not shown).

Transmission 10 includes a countershaft gearing arrangement 16 that includes intermediate shafts, a countershaft, co-planar intermeshing gear sets and selectively engagable synchronizers as will be described herein. For example, the countershaft gearing arrangement 16 includes a first intermediate shaft 18, a second intermediate shaft 20 and a third intermediate shaft 22. First, second and third intermediate shafts 18, 20 and 22 are sleeve shafts that are concentric with the input shaft 12. The countershaft gearing arrangement 16 further includes a first countershaft 24 and a second countershaft 26. Countershaft 24 is both spaced apart from and parallel with input shaft 12 and intermediate shafts 18, 20 and 22. Countershaft 26 is both spaced apart from and parallel with input shaft 12 and intermediate shafts 18, 20 and 22.

A first planetary gear set 28 and a second planetary gear set 30, which are simple planetary gear sets, are connected between the input shaft 12 and the output shaft 14. The first planetary gear set 28 includes sun gear member 32, a ring gear member 34 and a carrier member 36 which rotatably supports a set of pinion gears 38. The sun gear member 32 is rotationally fixed or connected for common rotation with the first intermediate shaft 18. The carrier member 36 is rotationally fixed or connected for common rotation with the second intermediate shaft 20. The ring gear 34 is rotationally fixed or connected for common rotation with the third intermediate shaft 22. The set of pinion gears 38 intermesh with both sun gear member 32 and the ring gear member 34. The second planetary gear set 30 includes sun gear member 40, a ring gear member 42 and a carrier member 44 which rotatably supports a set of pinion gears 46. The set of pinion gears 46 intermesh with both sun gear member 40 and the ring gear member 42. The ring gear 42 of the second planetary gear set 30 is connected for common rotation with the ring gear 34 of the first planetary gear set 28. The ring gear 42 of the second planetary gear set 30 and the ring gear 34 of the first planetary gear set 28 may be formed as a single unitary piece or as shown in FIG. 1 as two separate members connected by a shaft or hub. The carrier member 44 of the second planetary gear set 30 and carrier member 36 of the first planetary gear set 28 may be formed as a single unitary carrier member or as shown in FIG. 1 as two separate carrier members connected by shafts or hubs.

The countershaft gearing arrangement 16 also has co-planar, intermeshing gear sets 50, 60 and 70. Gear set 50 includes gears 52 and 54. Gear 52 is connected for common rotation with third intermediate shaft 22 and intermeshes with gear 54. Gear 54 is rotatable about and selectively connectable with the first countershaft 24.

Gear set 60 includes co-planar intermeshing gears 62 and 64. Gear 62 is connected for common rotation with the third intermediate shaft 22 and intermeshes with gear 64. Gear 64 is rotatable about and selectively connectable with the second countershaft 26.

Gear set 70 includes co-planar intermeshing gears 72, 74 and 76. Gear 72 is connected for common rotation with the first intermediate shaft 18 and intermeshes with gear 74 and gear 76. Gear 74 is rotatable about and selectively connectable with the first countershaft 24. Gear 76 is rotatable about and selectively connectable with the second countershaft 26.

Further, a first countershaft transfer gear 77 is rotatably fixed and connected for common rotation with the first countershaft 24. A second countershaft transfer gear 78 is rotatably fixed and connected for common rotation with the second countershaft 26. First countershaft transfer gear 77 and the second countershaft transfer gear 78 are each configured to mesh with an output transfer gear 79. The output transfer gear 79 is co-planar with first and second countershaft transfer gears 77, 78. However, the first countershaft transfer gear 77 and the second countershaft transfer gear 78 do not mesh with each other. The output transfer member 79 is attached to and rotatably drives output shaft 14. Accordingly, torque transmitted to countershaft 24 is transferred to transfer gear 77 and on to output shaft 14 via output transfer gear 79 and torque transmitted to countershaft 26 is transferred to transfer gear 78 and on to output shaft 14 via output transfer gear 79.

The transmission 10 includes a quadruple input clutch or assembly 80 having four torque-transmitting mechanisms or devices including a first input clutch 82, second input clutch 84, third input clutch 86 and fourth input clutch 88. Quadruple input clutch or assembly 80 has a clutch housing 90 fixedly connected for common rotation to the input shaft or member 12. Accordingly, first input clutch 82 is selectively engagable to connect the input shaft 12 with the ring gears 34 and 42 through the clutch housing 90. Second input clutch 84 is selectively engagable to connect the input shaft 12 with the carrier members 44 and 36 and second intermediate shaft 20 through the clutch housing 90. Third input clutch 86 is selectively engagable to connect the input shaft 12 with the sun gear 40 through the clutch housing 90. Fourth input clutch 88 is selectively engagable to connect the input shaft 12 with the sun gear 32 and first intermediate shaft 18 through the clutch housing 90.

Additionally, transmission 10 provides a brake member 92. Brake member 92 is selectively engagable to connect carrier members 36 and 44 through second intermediate shaft 20 to a stationary member such as the transmission housing 94 to restrict rotation of the carrier members 36 and 44.

The transmission 10 further includes a plurality of selectively engagable synchronizers 100, 102, 104 and 106. Synchronizer 100 is selectively engagable to connect second gear 54 of first co-planar gear set 50 with first countershaft 24 for common rotation therewith. Synchronizer 102 is selectively engagable to connect second gear 64 of second co-planar gear set 60 with second countershaft 26 for common rotation therewith. Synchronizer 104 is selectively engagable to connect second gear 74 of third co-planar gear set 70 with first countershaft 24 for common rotation therewith. Synchronizer 106 is selectively engagable to connect the third gear 76 of third co-planar gear set 70 to second countershaft 26 for common rotation therewith.

The transmission 10 is capable of transmitting torque from the input shaft 12 to the output shaft 14 in at least nine forward torque ratios and one reverse torque ratio as indicated in the truth table of FIG. 2. Each of the forward torque ratios and the reverse torque ratio is attained by engagement of one of the first, second, third torque-transmitting mechanisms or input clutches 82, 84, 86, 88, brake 92 and one or more of the synchronizers 100, 102, 104, and 106. Those skilled in the art will readily understand that a different speed ratio is associated with each torque ratio. Thus, nine forward speed ratios may be attained by the transmission 10.

To establish the reverse torque ratio (Gear State Rev), the input clutches, brake and synchronizers are selected as set forth in the table of FIG. 2. More specifically, input clutch 88, brake 92 and synchronizer 100 are engaged. The input clutch 88 connects the sun gear 32 of the first planetary gear set 28 with the input shaft 12. Synchronizer 100 connects second gear 54 for common rotation with first countershaft 24. Brake 92 connects carrier members 36 and 44 through second intermediate shaft 20 with transmission housing 94 for braking and preventing the rotation of carrier members 36 and 44. Torque is thus transferred from the input shaft 12 through the sun gear 32 to carrier members 36 and 44. Carrier members 36 and 44 transfer torque to the ring gears 34 and 42. Ring gears 34 and 42 transfer torque to third intermediate shaft 22. Third intermediate shaft 22 transfers torque to gear 52. Torque is transferred from gear 52 to gear 54. Gear 54 transfers torque to first countershaft 24 through synchronizer 100. Torque is then transferred from first countershaft 24 to the first countershaft transfer gear 77. First countershaft transfer gear 77 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a reverse gear ratio.

A first forward torque ratio (Gear State 1st in the truth table of FIG. 2), is achieved by engaging the input clutch 88 and synchronizer 104. The input clutch 88 connects the sun gear 32 of the first planetary gear set 28 with the input shaft 12. Synchronizer 104 connects second gear 74 for common rotation with first countershaft 24. Torque is thus transferred from the sun gear member 32 to first intermediate shaft 18 to gear 72. Torque is transferred from gear 72 to second gear 74. Second gear 74 transfers torque to first countershaft 24 through synchronizer 104. Torque is then transferred from first countershaft 24 to the first countershaft transfer gear 77. First countershaft transfer gear 77 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a first gear ratio.

A subsequent forward torque ratio, indicated as Gear State 2nd in FIG. 2, is established by engagement of input clutch 86 and synchronizers 100 and 104. The input clutch 86 connects the sun gear 40 of the second planetary gear set 30 with the input shaft 12. Synchronizer 100 connects second gear 54 for common rotation with first countershaft 24. Synchronizer 104 connects second gear 74 for common rotation with first countershaft 24. Torque is transferred from the input shaft 12 to sun gear 40 of the second planetary gear set 30 via the engaged input clutch 86. Torque then flows from sun gear 40 to carrier members 36 and 44 and from carrier members 36 and 44 to ring gears 34 and 42 and to the sun gear 32 of the first planetary gear set 28. Torque is transferred to gear 52 from third intermediate shaft 22 and to gear 72 from first intermediate shaft 18. Torque is transferred from gear 52 to gear 54 and from synchronizer 100 to first countershaft 24. Torque is transferred from gear 72 to gear 74 and from synchronizer 104 to first countershaft 24. Torque is then transferred from first countershaft 24 to the first countershaft transfer gear 77. First countershaft transfer gear 77 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a second gear ratio.

The subsequent torque ratio, indicated as Gear State 3rd in the truth table of FIG. 2, is established by the engagement of the input clutch 84 and synchronizers 100 and 104. The input clutch 84 connects the carrier members 36 and 44 with the input shaft 12. Synchronizer 100 connects second gear 54 for common rotation with first countershaft 24. Synchronizer 104 connects second gear 74 for common rotation with first countershaft 24. Torque is transferred from the input shaft 12 to carrier members 36 and 44 via the engaged input clutch 84. Torque then flows from carrier members 36 and 44 to ring gears 34 and 42 and sun gear 32 of the first planetary gear set 28. Torque is transferred from ring gears 34 and 42 to gear 52 via third intermediate shaft 22 and from sun gear 32 of the first planetary gear set 28 to gear 72 via first intermediate shaft 18. Torque is transferred from gear 52 to gear 54 and from synchronizer 100 to first countershaft 24. Torque is transferred from gear 72 to gear 74 and from synchronizer 104 to first countershaft 24. Torque is then transferred from first countershaft 24 to the first countershaft transfer gear 77. First countershaft transfer gear 77 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a third gear ratio.

The next subsequent forward torque ratio, indicated as Gear State 4th in the truth table of FIG. 2, is established with the engagement of the input clutch 82 and synchronizer 100. The input clutch 82 connects the ring gears 34 and 42 with the input shaft 12. Synchronizer 100 connects second gear 54 for common rotation with first countershaft 24. Torque is transferred from the input shaft 12 to ring gears 34 and 42 via the engaged input clutch 82. Torque is transferred from ring gears 34 and 42 to gear 52 via third intermediate shaft 22. Torque is transferred from gear 52 to gear 54 and from gear 54 to synchronizer 100 and from synchronizer 100 to first countershaft 24. Torque is then transferred from first countershaft 24 to the first countershaft transfer gear 77. First countershaft transfer gear 77 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a fourth gear ratio.

A subsequent forward torque ratio indicated as Gear State 5th in FIG. 2, is established with the engagement of input clutch 86 and synchronizers 100 and 106. The input clutch 86 connects the sun gear 40 of the second planetary gear set 30 with the input shaft 12. Synchronizer 100 connects second gear 54 for common rotation with first countershaft 24. Synchronizer 106 connects third gear 76 for common rotation with second countershaft 26. Torque is transferred from the input shaft 12 to sun gear 40 of the second planetary gear set 30 via the engaged input clutch 86. Torque then flows from sun gear 40 to carrier members 36 and 44 and from carrier members 36 and 44 to ring gears 34 and 42 and to the sun gear 32 of the first planetary gear set 28. Torque is transferred to gear 52 from third intermediate shaft 22 and to gear 72 from first intermediate shaft 18. Torque is transferred from gear 52 to gear 54 and from gear 54 to synchronizer 100 and to first countershaft 24. Torque is transferred from gear 72 to gear 76 and from gear 76 to synchronizer 106 and to second countershaft 26. Torque is then transferred from second countershaft 26 to the second countershaft transfer gear 78. Second countershaft transfer gear 78 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a fifth gear ratio.

A subsequent forward torque ratio indicated as Gear State 6th in the truth table of FIG. 2 is established with the engagement of input clutch 88 and synchronizer 106. The input clutch 88 connects the sun gear 32 of the first planetary gear set 28 with the input shaft 12. Synchronizer 106 connects third gear 76 for common rotation with second countershaft 26. Torque is thus transferred from the sun gear member 32 to gear 72 via first intermediate shaft 18. Torque is transferred from gear 72 to third gear 76. Third gear 76 transfers torque to second countershaft 26 through synchronizer 106. Torque is then transferred from second countershaft 26 to the second countershaft transfer gear 78. Second countershaft transfer gear 78 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a sixth gear ratio.

A subsequent forward torque ratio indicated as Gear State 7th in FIG. 2, is established with the engagement of input clutch 86 and synchronizers 102 and 106. The input clutch 86 connects the sun gear 40 of the second planetary gear set 30 with the input shaft 12. Synchronizer 102 connects second gear 64 for common rotation with second countershaft 26. Synchronizer 106 connects third gear 76 for common rotation with second countershaft 26. Torque is transferred from the input shaft 12 to sun gear 40 of the second planetary gear set 30 via the engaged input clutch 86. Torque then flows from sun gear 40 to carrier members 36 and 44 and from carrier members 36 and 44 to ring gears 34 and 42 and to the sun gear 32 of the first planetary gear set 28. Torque is transferred to gear 62 from third intermediate shaft 22 and to gear 72 from first intermediate shaft 18. Torque is transferred from gear 62 to gear 64 and from gear 64 to synchronizer 102 and to second countershaft 26. Torque is transferred from gear 72 to gear 76 and from gear 76 to synchronizer 106 and to second countershaft 26. Torque is then transferred from second countershaft 26 to the second countershaft transfer gear 78. Second countershaft transfer gear 78 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a seventh gear ratio.

The next subsequent forward torque ratio, indicated as Gear State 8th in the truth table of FIG. 2, is established with the engagement of the input clutch 84 and synchronizers 102 and 106. The input clutch 84 connects the carrier members 36 and 44 with the input shaft 12. Synchronizer 102 connects second gear 64 for common rotation with second countershaft 26. Synchronizer 106 connects third gear 76 for common rotation with second countershaft 26. Torque is transferred from the input shaft 12 to carrier members 36 and 44 via the engaged input clutch 84. Torque then flows from carrier members 36 and 44 to ring gears 34 and 42 and sun gear 32 of the first planetary gear set 28. Torque is transferred from ring gears 34 and 42 to gear 62 via third intermediate shaft 22 and from sun gear 32 of the first planetary gear set 28 to gear 72 via first intermediate shaft 18. Torque is transferred from gear 62 to gear 64 and from synchronizer 102 to second countershaft 26. Torque is transferred from gear 72 to gear 76 and from synchronizer 106 to second countershaft 26. Torque is then transferred from second countershaft 26 to the second countershaft transfer gear 78. Second countershaft transfer gear 78 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce an eighth gear ratio.

The next subsequent forward torque ratio, indicated as Gear State 9th in the truth table of FIG. 2, is established with the engagement of the input clutch 82 and synchronizer 102. The input clutch 82 connects the ring gears 34 and 42 with the input shaft 12. Synchronizer 102 connects second gear 64 for common rotation with second countershaft 26. Torque is transferred from the input shaft 12 to ring gears 34 and 42 via the engaged input clutch 82. Torque is transferred from ring gears 34 and 42 to gear 62 via third intermediate shaft 22. Torque is transferred from gear 62 to gear 64 and from synchronizer 102 to second countershaft 26. Torque is then transferred from second countershaft 26 to the second countershaft transfer gear 78. Second countershaft transfer gear 78 transfers the torque to the output shaft 14 via the output transfer gear 79 to produce a ninth gear ratio.

The present invention contemplates that downshifts follow essentially the reverse sequence of the corresponding upshift (as described above), and several power-on skip-shifts are possible.

Referring now to FIG. 3 a nine speed transmission 100 is depicted according to the principles of the invention. The transmission 100 has the same components as described previously with respect to transmission 10 and as indicated in FIG. 3 with like reference numbers. However, transmission 100 has a different special arrangement for co-planar gear set 50, herein referenced as co-planar gear set 50′, co-planar gear set 60, herein referenced as co-planar gear set 60′ and co-planar gear set 70, herein referenced as co-planar gear set 70′. Co-planar gear set 70′ is now located closest to the input clutch 80. Co-planar gear set 60′ is now located furthest from input clutch 80. Co-planar gear set 50′ is now disposed between co-planar gear sets 60′ and 70′. More specifically, gear set 50′ includes co-planar intermeshing gears 52′ and 54′. Gear set 60′ includes co-planar intermeshing gears 62′ and 64′. Gear set 70′ includes co-planar intermeshing gears 72′, 74′ and 76′, where gear 72′ intermeshes with both gears 74′ and 76′. Gear 52′ and 62′ are connected for common rotation with the first intermediate shaft 18. Gears 54′ and 74′ are rotatable about and selectively connectable with the first countershaft 24. Gears 64′ and 76′ are rotatable about and selectively connectable with the second countershaft 26. Synchronizer 100 selectively engages gear 74′ to first countershaft 24 for common rotation therewith instead of selectively connecting gear 54 to first countershaft 24, as described above with respect to transmission 10. Synchronizer 102 selectively engages gear 76′ to second countershaft 26 for common rotation therewith instead of selectively connecting gear 64 to second countershaft 26, as described above with respect to transmission 10. Synchronizer 104 selectively engages gear 54′ to first countershaft 24 for common rotation therewith instead of selectively connecting gear 74 to first countershaft 24, as described above with respect to transmission 10. Synchronizer 106 selectively engages gear 64′ to second countershaft 26 for common rotation therewith instead of selectively connecting gear 76 to second countershaft 26, as described above with respect to transmission 10.

The transmission 100 is capable of transmitting torque from the input shaft 12 to the output shaft 14 in at least nine forward torque ratios and one reverse torque ratio as indicated in the truth table of FIG. 4. Each of the forward torque ratios and the reverse torque ratio is attained by engagement of one of the first, second, third and fourth torque-transmitting mechanisms or input clutches 82, 84, 86, 88, brake 92 and one or more of the synchronizers 100, 102, 104 and 106 as indicated by an “X” in the columns of the truth table of FIG. 4. Those skilled in the art will readily understand that a different speed ratio is associated with each torque ratio. Thus, nine forward speed ratios may be attained by the transmission 100.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. A transmission comprising: an input member; an output member; a first planetary gear set having first, second and third members; a second planetary gear set having first, second and third members wherein the second member of the first planetary gear set is connected to the second member of the second planetary gear set and the third member of the first planetary gear set is connected to the third member of the second planetary gear set; a clutch assembly having a first, a second, a third and a fourth torque-transmitting mechanism each selectively engageable to connect the input member with a respective different one of the members of the first and second planetary gear sets; a first intermediate shaft connected for common rotation with the first member of the first planetary gear set; a second intermediate shaft connected for common rotation with the second members of the first and second planetary gear sets, wherein the second intermediate shaft is concentric with the first intermediate shaft; a third intermediate shaft connected for common rotation with the third members of the first and second planetary gear sets, wherein the third intermediate shaft is concentric with the second intermediate shaft; a first countershaft radially offset from the intermediate shafts; a second countershaft radially offset from the intermediate shafts; a first countershaft transfer gear connected for common rotation with the first countershaft and in communication with the output member to transfer torque from the first countershaft to the output member; a second countershaft transfer gear connected for common rotation with the second countershaft and in communication with the output member to transfer torque from the second countershaft to the output member; at least three co-planar intermeshing gear sets, wherein at least one of the gears of the at least three co-planar intermeshing gear sets is fixed for common rotation with at least one of the intermediate shafts; and a plurality of synchronizers, wherein at least one of the plurality of synchronizers is selectively engagable to connect at least one of the gears of the at least three co-planar intermeshing gear sets with at least one of the first and second countershafts for common rotation therewith, thereby transferring torque from the first and second planetary gear sets to at least one of the first and second countershafts through at least one of the intermediate shafts and at least one of the sets of co-planar intermeshing gear sets.
 2. The transmission of claim 1 wherein the first members of the first and second planetary gear sets are sun gears, the second members of the first and second planetary gear sets are planet carrier members and third members of the first and second planetary gear sets are ring gears.
 3. The transmission of claim 2 wherein the planet carrier member of the first planetary gear set rotatably supports a set of planet gears and wherein the set of planet gears intermeshes with the sun gear and the ring gear of the first planetary gear set and the planet carrier member of the second planetary gear set rotatably supports a set of planet gears and wherein the set of planet gears intermeshes with the sun gear and the ring gear of the second planetary gear set.
 4. The transmission of claim 2 wherein the first intermediate shaft is connected for common rotation with sun gear of the first planetary gear set.
 5. The transmission of claim 2 wherein the second intermediate shaft is connected for common rotation with the planet carrier members of the first and second planetary gear sets.
 6. The transmission of claim 2 wherein the first torque-transmitting mechanism is selectively engageable to connect the input member with the ring gears of the first and second planetary gear sets, the second torque-transmitting mechanism is selectively engageable to connect the input member with the planet carriers of the first and second planetary gear sets, the third torque-transmitting mechanism is selectively engageable to connect the input member with the sun gear of the second planetary gear set and the fourth torque-transmitting mechanism is selectively engageable to connect the input member with the sun gear of the first planetary gear set.
 7. The transmission of claim 1 wherein two of the at least three co-planar intermeshing gear sets each include a first gear in mesh with a second gear.
 8. The transmission of claim 7 wherein one of the at least three co-planar intermeshing gear sets includes a first gear in mesh with a second gear and a third gear.
 9. The transmission of claim 8 wherein the first gear of one of the at least three co-planar intermeshing gear sets is fixedly connected to the first intermediate shaft and the first gears of the other two of the at least three co-planar intermeshing gear sets are fixedly connected to the third intermediate shaft.
 10. The transmission of claim 8 wherein the second gears of two of the at least three co-planar intermeshing gear sets are selectively engageable with the first countershaft and the second gear of the remaining one of the at least three co-planar intermeshing gear sets is selectively engageable with the second countershaft.
 11. The transmission of claim 1 wherein the plurality of synchronizers further includes a first synchronizer for selectively connecting a second gear of a first of the at least three co-planar intermeshing gear sets with the first countershaft.
 12. The transmission of claim 11 wherein the plurality of synchronizers further includes a second synchronizer for selectively connecting a second gear of the second of the at least three co-planar intermeshing gear sets with the second countershaft.
 13. The transmission of claim 12 wherein the plurality of synchronizers further includes a third synchronizer for selectively connecting a second gear of a third of the at least three co-planar intermeshing gear sets with the first countershaft.
 14. The transmission of claim 13 wherein the plurality of synchronizers further includes a fourth synchronizer for selectively connecting a third gear of the third of the at least three co-planar intermeshing gear sets with the second countershaft.
 15. The transmission of claim 14 wherein the plurality of synchronizers further comprises a brake for selectively connecting the carrier members of the first and second planetary gear sets with a stationary member.
 16. The transmission of claim 1 wherein the output member further includes an output transfer gear in mesh with each of the first and second countershaft transfer gears.
 17. A transmission comprising: an input member; an output member; a first planetary gear set having a sun gear, a carrier member and ring gear, wherein the carrier member rotatably supports a set of planet pinion gears that intermesh with both the sun gear and the ring gear of the first planetary gear set; a second planetary gear set having a sun gear, a carrier member and a ring gear, wherein the carrier member of the second planetary gear set rotatably supports a set of planet pinion gears that intermesh with both the sun gear and the ring gear of the second planetary gear set and wherein the carrier member of the first planetary gear set is connected to the carrier member of the second planetary gear set and the ring gear of the first planetary gear set is connected to the ring gear of the second planetary gear set and wherein the carrier; a clutch assembly having a first, a second, a third and a fourth clutch, wherein the first clutch is selectively engageable to connect the input member with the ring gears of the first and second planetary gear sets, the second clutch is selectively engageable to connect the input member with the carrier members of the first and second planetary gear sets, the third clutch is selectively engageable to connect the input member with the sun gear of the second planetary gear set and the fourth clutch is selectively engageable to connect the input member with the sun gear of the first planetary gear set; a first intermediate shaft connected for common rotation with the sun gear of the first planetary gear set, wherein the first intermediate shaft is concentric with the input shaft; a second intermediate shaft connected for common rotation with the carrier members of the first and second planetary gear sets, wherein the second intermediate shaft is concentric with the first intermediate shaft; a third intermediate shaft connected for common rotation with the ring gears of the first and second planetary gear sets, wherein the third intermediate shaft is concentric with the second intermediate shaft; a first countershaft radially offset from the intermediate shafts and in communication with the output member; a second countershaft radially offset from the intermediate shafts and in communication with the output member; a first, second and third co-planar intermeshing gear sets, wherein the first and second co-planar intermeshing gear sets each having a first gear intermeshing with a second gear and a third gear and the third co-planar intermeshing gear set has a first gear intermeshing with a second gear, wherein the first gears of the first and second co-planar intermeshing gear sets are fixed for common rotation with the third intermediate shaft and the first gear of the third co-planar intermeshing gear set is fixed for common rotation with the first intermediate shaft; and a plurality of synchronizers, wherein each of the plurality of synchronizers is selectively engagable to connect at least one of the gears of the at least three co-planar intermeshing gear sets with at least one of the first and second countershafts for common rotation therewith, thereby transferring torque from the first and second planetary gear sets to at least one of the first and second countershafts through at least one of the intermediate shafts and at least one of the sets of co-planar intermeshing gear sets.
 18. The transmission of claim 17 wherein the plurality of synchronizers further includes a first synchronizer for selectively connecting a second gear of a first of the at least three co-planar intermeshing gear sets with the first countershaft.
 19. The transmission of claim 18 wherein the plurality of synchronizers further includes a second synchronizer for selectively connecting a second gear of the second of the at least three co-planar intermeshing gear sets with the second countershaft.
 20. The transmission of claim 19 wherein the plurality of synchronizers further includes a third synchronizer for selectively connecting a second gear of a third of the at least three co-planar intermeshing gear sets with the first countershaft.
 21. The transmission of claim 20 wherein the plurality of synchronizers further includes a fourth synchronizer for selectively connecting a third gear of the third of the at least three co-planar intermeshing gear sets with the second countershaft.
 22. The transmission of claim 21 wherein the plurality of synchronizers further comprises a brake for selectively connecting the carrier members of the first and second planetary gear sets with a stationary member.
 23. The transmission of claim 17 further comprising first and second countershaft transfer gears, wherein the first countershaft transfer gear is rotatably fixed for common rotation with the first countershaft and the second countershaft transfer gear is rotatably fixed for common rotation with the second countershaft.
 24. The transmission of claim 23 wherein the output member further includes an output transfer gear in mesh with each of the first and second countershaft transfer gears. 